1. Field of the Invention
The present invention relates to a resin product comprises a metal film such as metallic gloss film having a discontinuous structure and a process for producing the same, and a process for forming the metal film. The product is applied to various uses such as a millimeter-wave radar device cover.
2. Related Art
In order to give a driver a warning that his car comes close to a surrounding article, it has been investigated to provide a millimeter-wave radar device for distance measurement on some parts of the car, e.g., a radiator grill, a side mall, and a back panel. However, in the case that the radiator grill and the like are those having metallic gloss with a metal film, the metal film blocks or remarkably attenuates the millimeter wave. Therefore, it is necessary to cover the path of the millimeter wave of the radar device with a cover with metallic gloss and millimeter-wave-transparency for a radar device cover. In order to have millimeter-wave transparency, the metal film should have a discontinuous structure, i.e., a structure (island-like morphology) wherein the metal film is not continuous over a whole surface and a large number of fine metal films are bedded in a state that they are slightly separated from each other as islands.
In conventional millimeter-wave radar device covers, the metallic gloss film having a discontinuous structure is formed by vacuum deposition of a single metal such as In (JP-A-2000-159039 and JP-A-2000-344032 etc.). This is because a metal such as In has a property of being apt to form a discontinuous structure. Even if most of metals poor in such a property are subjected to film formation by vacuum deposition, the film structure is changed into a continuous structure to lower electric resistance and to result in insufficient millimeter-wave transparency when a film thickness region affording an apparently sufficient metallic gloss is achieved.
However, In is particularly expensive and hence there is a problem that a product cost increases. Thus, reduction of an amount of In to be used and use of a metal other than In are required.